Cut off stalk and root from beets and cut large beets in half.
Mix sugar, vinegar, water and pickling spices.
Bring to a boil and add the beets.
Cook until the beets are soft. (They are done when a fork easily pushes into them.)
Remove beets from liquid, but save the liquid.
Slide the skin off the beets and slice evenly. (I use an egg slicer.)
If using, mix in some thinly sliced red onion.
Put beets and onion (if using) in jars, pour the liquid over them and seal.